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Monoclinal Flexure of an Orogenic Plateau Margin During Subduction, South Turkey

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Monoclinal Flexure of an Orogenic Plateau Margin During Subduction, South Turkey Non-peer reviewed preprint submitted to EarthArXiv Monoclinal flexure of an orogenic plateau margin during subduction, south Turkey Running title: Monoclinal flexure plateau margin David Fernández-Blanco1, Giovanni Bertotti2, Ali Aksu3 and Jeremy Hall3 1Tectonics and Structural Geology Department, Faculty of Earth and Life Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands [email protected] 2Department of Geotechnology, Faculty of Civil Engineering and Geosciences, Delft University of Technology, Stevinweg 1, 2628CN, Delft, the Netherlands 3 Department of Earth Sciences, Centre for Earth Resources Research, Memorial University of Newfoundland, St. John's, Newfoundland, Canada A1B 3X5 Non-peer reviewed preprint submitted to EarthArXiv Abstract Geologic evidence across orogenic plateau margins helps to discriminate the relative contributions of orogenic, epeirogenic and/or climatic processes leading to growth and maintenance of orogenic plateaus and plateau margins. Here, we discuss the mode of formation of the southern margin of the Central Anatolian Plateau (SCAP), and evaluate its time of formation, using fieldwork in the onshore and seismic reflection data in the offshore. In the onshore, uplifted Miocene rocks in a dip-slope topography show monocline flexure over >100 km, few-km asymmetric folds verging south, and outcrop- scale syn-sedimentary reverse faults. On the Turkish shelf, vertical faults transect the basal latest Messinian of a ~10 km fold where on-structure syntectonic wedges and synsedimentary unconformities indicate pre-Pliocene uplift and erosion followed by Pliocene and younger deformation. Collectively, Miocene rocks delineate a flexural monocline at plateau margin scale, expressed along our on-offshore sections as a kink- band fold with a steep flank ~20–25 km long. In these reconstructed sections, we estimate a relative vertical displacement of ~3.8 km at rates of ~0.5 mm/y, and horizontal shortening values <1 %. We use this evidence together with our observations of shortening at outcrop, basin, plateau-margin and forearc system scales to infer that the SCAP forms as a monoclinal flexure to accommodate deep-seated thickening and shortening since >5 Ma, and to contextualize the plateau margin as the forearc high of the Cyprus subduction system. Keywords: orogenic plateau; Anatolian plateau; plateau margin; south Turkey; monocline; Mut Basin; Cilicia Basin 2 Non-peer reviewed preprint submitted to EarthArXiv 1. Introduction Many mechanisms are proposed to explain the growth of orogenic plateaus and the long- term feedbacks between their geodynamic and/or climatic controls (e.g., Bird, 1979; Powell, 1986; Nelson et al., 1996; Pope & Willett, 1998; Yin & Harrison, 2000; Tapponnier et al., 2001; Şengör et al., 2003; Sobel et al., 2003; Rowley & Currie, 2006; Garcia- Castellanos, 2007; Ballato et al., 2010; Biryol et al., 2011). While tectono-structural and thermo-mechanical models relate plateau margin growth to accretion/removal of crustal or lithospheric material, magmatic/tectonic underplating or rheological changes (e.g., Allmendinger et al., 1997; Clark, 2012), the climatic-erodibility models relate the tectonic activity to climate, rock erodibility, and precipitation power during incipient relief development (e.g., Mulch et al., 2006; Strecker et al., 2009). Geologic data across plateau margins (on- and offshore) is pivotal to understand plateau margin growth and explain certain features that are not always entirely captured by these models. Current studies advocate for epeirogenic causes to explain the growth and uplift of the Central Anatolian Plateau southern margin (SCAP) (e.g., Schildgen et al., 2014). Shallow slab break-off and asthenospheric mantle upwelling are proposed as engines for the post-8 Ma surface uplift of the modern Central Taurides, occurring either separately from (Cosentino et al., 2012), or jointly with, a second uplift phase, with rates of 0.6-0.7 mm/yr and leading to ~1200 m of topography, after ~1.6 Ma (Schildgen et al., 2012), and a new uplift phase, with rates of 3.21-3.42 mm/yr and leading to up to 1500 m of topography, since ~450 ka (Öğretmen et al., 2018). For these studies, the Central Taurides surface uplift is “passive” and detached from regional compression due to subduction (e.g., Schildgen et al., 2014). Epeirogenic models of plateau uplift that might apply in the Central Anatolia Plateau 3 Non-peer reviewed preprint submitted to EarthArXiv interior (e.g., Bartol & Govers, 2014; Göğüş et al., 2017) are at variance with geologic evidence farther south. For example, the Cyprus slab is imaged by tomography along the Central Cyprus subduction zone and below the modern Central Taurides (e.g., Bakırcı et al., 2012; Abgarmi et al., 2017), where a thick crust and mantle lithosphere exist (e.g., Delph et al., 2017; Portner et al., 2018). Also, the concomitance of uplift in the modern Central Taurides and subsidence in the offshore Outer Cilicia Basin (OCB) to the south (e.g., Walsh-Kennedy et al., 2014) indicate short-wavelength vertical motions in the long- term, at odds with the long-wavelength vertical motions expected during asthenospheric upwelling (e.g., Göğüş & Pysklywec, 2008). Stable isotope paleoaltimetry estimates suggest that ~2 km of relief existed at ~5 Ma (Meijers et al., 2018), a finding also at odds with models proposing epeirogenic uplift. Finally, compressional tectonics of the Cyprian subduction zone is attested by tapering-southward forearc basins atop south-verging thrust systems in the offshore (e.g., Aksu et al., 2005a, 2005b; Calon et al., 2005a, 2005b; Hall et al., 2005a, 2005b), in the Kyrenia Range, and in the Messaoria Basin (e.g., McCay, 2010; McCay & Robertson, 2012; McCay et al., 2012). These observations provide a different frame whereby the southern margin of the Central Anatolian Plateau may have been uplifted “actively” by contraction within the Cyprus subduction system. Here, we apply a multi-scale approach and consider the SCAP within the larger context of subduction in the Central Cyprus Arc. We analyse key fieldwork observations in the Mut Basin, lying atop the Tauride Mountains to the north, and interpret and depth- convert N-S trending seismic lines in the offshore Outer Cilicia Basin (OCB) (Fig. 1). We link these basins in regional onshore-offshore cross-sections to delineate a monocline at plateau margin scale that we analyse geometrically. Integrating this with our data along the Central Cyprus forearc, we evaluate the time of formation of the plateau margin, and discuss its growth mechanism, tectonic setting and potential geodynamic drivers. 4 Non-peer reviewed preprint submitted to EarthArXiv 2. Background A broad Miocene subsidence initiated marine deposition and led to a wide basin in the NE Mediterranean (e.g., Walsh-Kennedy et al., 2014). This regional event allows for regional correlations across onshore and offshore sites in our region of study (Fig. 2). Whereas subsidence continued until present in the Cilicia Basin (in the centre of the marine basin), the basin was disrupted by uplift in the Central Taurides (to the north) (e.g., Cosentino et al., 2012), in the Kyrenia Range and to the south (e.g., Calon et al., 2005a) (Fig. 3). Such vertical motions exceed glacio-eustatic signals described for the area (e.g., Bassant et al., 2005; Janson et al., 2010; Cipollari et al., 2013) and should be regarded as portraying two different tectonic events, i.e. protracted regional subsidence since the Early Miocene, and Late Miocene differential motions (Fig. 3). The broad subsidence changed Late Oligocene-Early Miocene continental deposition in Anatolia and surrounding regions (e.g., Yetiş et al., 1995; Clark & Robertson, 2002, 2005) to marine deposition (e.g., Robertson, 1998; Bassant et al., 2005; Eriş et al., 2005; Şafak et al., 2005). Continued subsidence resulted in a broad marine basin (e.g., Walsh- Kennedy et al., 2014) that covered south Turkey (Karabıyıkoğlu et al., 2000; Çıner et al., 2008) (Fig. 1) and an extensive area further south (Aksu et al., 2005a, 2005b; Burton- Ferguson et al., 2005; Hall et al., 2005a; Işler et al., 2005). In the vicinity of the Kyrenia Range, deposition of the mostly deep-water upper Oligocene to upper Miocene sequence preceded shallow deposits, broadly similar to basins to the north and north-east, and with a common Tauride source (McCay & Robertson, 2012). Surface uplift to the north exposes a sedimentary sequence of >1 km (Şafak et al., 2005) of the preceding Miocene basin on top of the Central Taurides. The top of this sequence is uplifted by 2 km and dated as ∼8 Ma, Late Tortonian (Cosentino et al., 2012), 5 Non-peer reviewed preprint submitted to EarthArXiv whereas younger rocks outcrop in paleo-valleys and areas near the coast (Öğretmen et al., 2018). In the offshore to the south, the base of the Messinian reaches ∼2 km depth in the Outer Cilicia Basin (OCB) (Aksu et al., 2005a). Farther south, sedimentary deposits belonging to the preceding Miocene basin now outcrop in the Kyrenia Ridge (Calon et al., 2005b; McCay et al., 2012) (Fig. 3). While south-verging contractional structures accommodate these motions in the Kyrenia Range and further south, no regional upper- crustal structures are known to accommodate uplift in the Central Taurides. 2.1 Northern onshore domain: Central Taurides and Mut Basin The E-W south-arched Central Taurides outcrop in the northern onshore domain, to the north of the OCB (Fig. 1). Lower to Upper Miocene sediments, mostly marine, were deposited atop the pre-Miocene Tauride basement (e.g., Monod, 1977; Andrew & Robertson, 2002; Bassant et al., 2005; Eriş et al., 2005) and then uplifted (Fig. 3). These marine sediments belong to the Mut Basin and are coeval with fluvio-lacustrine deposits known from seismics for the Tuz Gölü area farther north (Gorur et al., 1984; Huvaz, 2009; Fernández-Blanco et al., 2013). Rocks in both areas are in turn unconformably covered by terrace and alluvial fan Pliocene to Quaternary continental deposits (Monod et al., 2006; Özsayin et al., 2013) (Fig.
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